Semiconductor structure

ABSTRACT

A semiconductor structure includes a substrate, a fin, a bottom capping structure and a top capping structure. The fin disposed on the substrate, the fin has a lower portion and an upper portion extending upwards from the lower portion. The bottom capping structure covers a sidewall of the lower portion of the fin. The top capping structure covers a sidewall of the upper portion of the fin.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. patent application Ser. No. 16/186,783, filed Nov. 12, 2018, now U.S. Pat. No. 10,665,191, issued May 26, 2020, which is a divisional application of U.S. patent application Ser. No. 15/409,617, filed Jan. 19, 2017, now U.S. Pat. No. 10,134,870, issued Nov. 20, 2018, which claims priority to U.S. Provisional Application Ser. No. 62/426,667, filed Nov. 28, 2016, all of which are herein incorporated by reference in their entireties.

BACKGROUND

The semiconductor integrated circuit industry has experienced rapid growth in the past several decades. Technological advances in semiconductor materials and designs have produced increasingly smaller and more complex circuits. These material and design advances have been made possible as the technologies related to processing and manufacturing have also undergone technical advances. In the course of semiconductor evolution, the number of interconnected devices per unit of area has increased as the feature size has decreased. The semiconductor integrated circuit industry has produced numerous developments in effort to continue the process of scaling. One of the developments is the replacement or supplementation of the conventional planar metal-oxide-semiconductor field-effect transistor by the vertical field-effect transistor. However, existing vertical field-effect transistors have not been satisfactory in all aspects.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion.

FIG. 1 is a flowchart illustrating a method of fabricating a semiconductor structure according to some embodiments of the present disclosure.

FIGS. 2-9 are cross sectional views illustrating various stages of the method according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

In conventional FINFET fabrications, liners or capping layers are formed covering the fins in order to protect the fins from oxidation and/or degradation in subsequent processes. Various liners or capping layers, such as silicon nitride (SiN) and/or siliconborocarbonitride (SiBCN) have been used in the manufacturing of the semiconductor devices. However, conventional liners or capping layers suffers some problems such as the so-called “dishing” in shallow trench isolation (STI) structures.

The present disclosure relates generally to a semiconductor structure and the manufacturing method thereof. According to some embodiments of the present disclosure, the semiconductor structure and the method disclosed herein may mitigate or even resolve the issues discussed above. Although embodiments hereinafter are discussed in a particular order, various other embodiments may be performed in any logical order and may include fewer or more steps described herein.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of the embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present.

FIG. 1 is a flowchart illustrating a method 100 of manufacturing a semiconductor structure 200 according to some embodiments of the present disclosure. FIGS. 2-9 are cross sectional views illustrating various stages of the method 100 according to some embodiments of the present disclosure. It is understood that additional steps can be provided before, during, and/or after the method 100, and some of the steps described can be replaced, eliminated, and/or moved around for additional embodiments of the method 100.

Referring now to FIGS. 1 and 2, the method 100 begins at operation 110 by forming a fin on a substrate. FIG. 2 illustrates the formation of a fin 220 and a fin 230 on a substrate 210 according to some embodiments. In some embodiments, the substrate 210 has a PMOS region 212 and a NMOS region 214 thereon. The fins 220, 230 are respectively formed on the PMOS region 212 and the NMOS region 214. The fin 220 and fin 230 have respective lower portions 222, 232 and respective upper portions 224, 234. In some embodiments, the fin 220 and fin 230 are similar in structure and material. For example, the lower portions 222, 232 and the upper portions 224, 234 of the fins 220, 230 are made of silicon. In yet some embodiments, each of the fins 220, 230 may include composite material. Specifically, the lower portions 222, 232 of the fins 220, 230 may include silicon or consist essentially of silicon with or without dopants, but the upper portions 224, 234 of the fins 220, 230 may include silicon germanium or consist essentially of silicon germanium with or without dopants. In yet some embodiments, however, the material of the fin 220 formed on the PMOS region 212 may differ from that of the fin 230 formed on the NMOS region 214. Specifically, both the lower and upper portions 232, 234 of the fin 230 may include silicon or consist essentially of silicon, whereas the upper portion 224 of the fin 220 is made of silicon germanium while the lower portion 222 of the fin 220 is made of silicon. In some examples, the upper portion 224 of the fin 220 has a germanium molar concentration ranged from about 10% to about 35%, such as for example 15%, 20%, 25%, and 30%. One skilled in the art readily understands that the fins 220, 230 are shown for the illustrative purpose only, and more fins may be formed on the substrate 210.

In some embodiments, the fins 220, 230 may be fabricated using suitable processes including photolithography and etch processes. The photolithography process may include forming a photoresist layer (resist) overlying the substrate (e.g., on a silicon layer), exposing the resist by a patterned mask, performing post-exposure bake processes, and developing the resist to form a masking layer. An etching process may be carried out using the masking layer to form the fins 220, 230. Illustrative examples of the etching process include wet etching techniques and/or dry etching techniques such as plasma etching techniques, reactive ion etch (RIE) techniques and other suitable techniques.

In some embodiment, the fins 220, 230 may be formed by double-patterning lithography (DPL) process. DPL is a method of constructing a pattern on a substrate by dividing the pattern into two interleaved patterns. DPL allows to enhance feature (e.g., fin) densities. Various DPL methodologies that may be used include double exposure (e.g., using two mask sets), forming spacers adjacent features and removing the features to provide a pattern of spacers, resist freezing, and/or other suitable processes.

One skilled in the art readily understands that the processes described above are just examples of the formation of the fins 220, 230. In other embodiments, a dielectric layer may be formed over a top surface of the substrate 210; trenches may be formed in the dielectric layer; homoepitaxial structures may be epitaxially grown in the trenches; and the dielectric layer may be recessed such that the homoepitaxial structures protrude from the dielectric layer to form the fins 220, 230. In still other embodiments, heteroepitaxial structures may be used for the fins 220, 230. In an even further embodiment, a dielectric layer may be formed over a top surface of the substrate 210; trenches may be formed in the dielectric layer; heteroepitaxial structures may be epitaxially grown in the trenches using a material different from the substrate 210; and the dielectric layer may be recessed such that the heteroepitaxial structures protrude from the dielectric layer to form the fins 220, 230. In some embodiments where homoepitaxial or heteroepitaxial structures are epitaxially grown, the grown materials may be in situ doped during growth, which may obviate prior and subsequent implantations although in situ and implantation doping may be used together.

The substrate 210 may be a semiconductor substrate, such as a semiconductor-on-insulator (SOT) substrate, a bulk semiconductor, or the like. Alternatively, the substrate may be a wafer, such as a silicon wafer. The SOI substrate may include a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a silicon oxide layer, a buried oxide (BOX) layer, or the like. Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of the substrate may include silicon; germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, AlInAs, GaAsP, AlGaAs, GaInP, GalnAs and/or GaInAsP; or combinations thereof.

The substrate 210 may include active devices (not shown) or passive devices (not shown) that may be used to generate the desired structural and functional parts of the design. The active devices may include a wide variety of active devices such as transistors, and the like. The passive devices, for example, may be capacitors, resistors, inductors, and the like. The active devices and passive devices may be formed using any suitable methods either within or else on the substrate 210.

Referring now to FIGS. 1 and 3, the method 100 proceeds to operation 120 by forming a nitridized capping layer covering the fin. FIG. 3 illustrates the deposition of a nitridized capping layer 310 a that conformally covers the fins 220, 230 according to some embodiments of the present disclosure. The nitridized capping layer 310 a may be formed by various approaches. In some embodiments, a capping material layer 310 is first deposited to cover the substrate 210, the fin 220 and the fin 230. The capping material layer 310 may include or consist essentially of silicon, for example. After forming the capping material layer 310, a nitridation treatment is carried out to transform the capping material layer 310 into the nitridized capping layer 310 a, in accordance with some embodiments. The nitridation treatment may be a rapid thermal nitridation (RTN) process and/or other suitable processes such as nitrogen implantation techniques. In some examples, the nitridized capping layer 310 a has a nitrogen molar percentage of less than 12 mol %. For instance, the nitrogen molar percentage of the nitridized capping layer 310 a may be ranged from about 2 mol % to about 8 mol %, such as 3 mol %, 4 mol %, 5 mol %, 6 mol %, and 7 mol %. The capping material layer 310 may be formed by suitable approaches such as chemical vapor deposition (CVD) processes, sub-atmospheric CVD (SACVD) processes, flowable CVD processes, atomic layer deposition (ALD) processes, physical vapor deposition (PVD) processes, and/or other suitable processes. In yet some embodiments, the capping material layer 310 may be formed by epitaxial growth processes, such as a molecular beam epitaxial (MBE) process, a metalorganic chemical vapor deposition (MOCVD) process, and/or other suitable epitaxial growth processes.

Referring now to FIGS. 1 and 4, the method 100 proceeds to operation 130 by forming a nitridized oxide layer covering nitridized capping layer. FIG. 4 illustrates the formation of a nitridized oxide layer 410 a conformally covering the nitridized capping layer 310 a. The nitridized oxide layer 410 a may be formed by various approaches. In some embodiments, a first oxide layer 410 is first deposited to conformally cover the nitridized capping layer 310 a. For example, the first oxide layer 410 may include SiO₂ or other suitable oxide materials. Thereafter, the first oxide layer 410 is nitridized to form the nitridized oxide layer 410 a. The first oxide layer 410 may be nitridized by various processes such as rapid thermal nitridation (RTN) processes and/or other suitable processes such as nitrogen implantation techniques. In some examples, the nitridized oxide layer 410 a has a nitrogen molar percentage of less than 12 mol %. For example, the nitrogen molar percentage of the nitridized oxide layer 410 a may be ranged from about 2 mol % to about 8 mol %, such as 3 mol %, 4 mol %, 5 mol %, 6 mol %, and 7 mol %. The first oxide layer 410 may be deposited by suitable approaches such as chemical vapor deposition (CVD) processes, sub-atmospheric CVD (SACVD) processes, flowable CVD processes, atomic layer deposition. (ALD) processes, physical vapor deposition (PVD) processes, and/or other suitable process.

Referring now to FIGS. 1 and 5, the method 100 proceeds to operation 140 by forming a dielectric layer over the nitridized oxide layer. FIG. 5 illustrates the formation of a dielectric layer 510 over the nitridized oxide layer 410 a according to some embodiments. The dielectric layer 510 may be formed by a chemical vapor deposition (CVD) process, a sub-atmospheric CVD (SACVD) process, a flowable CVD process, an atomic layer deposition (ALD) process, a physical vapor deposition (PVD) process, and/or other suitable processes. In examples, the dielectric layer 510 includes a layer of silicon oxide formed by a flowable CVD process. Nevertheless, other dielectric materials formed by any acceptable process may be used. In yet some embodiments, a first annealing process may be performed to densify the deposited dielectric layer 510. Thereafter, a planarization process (e.g., a chemical mechanical polishing process) may optionally be carried out to remove an excessing portion of the dielectric layer 510, thereby exposing the top surfaces of the fins 220, 230. In some embodiments, a second annealing process may be performed to improve the quality of the dielectric layer 510 after the planarization process. Illustrative examples of the first and second annealing processes include rapid thermal anneal (RTA) processes, single strand anneal (SSA) processes, laser anneal processes, flash anneal processes, furnace anneal processes, and/or other suitable processes. It is noted that the composition of the dielectric layer 510 is different from that of the nitridized oxide layer 410 a. In some embodiments, the difference in nitrogen molar percentage between the dielectric layer 510 and the nitridized oxide layer 410 a may be ranged from about 1 mol % to about 12 mol %, specifically about 2 mol % to about 10 mol %, more specifically 2 mol % to about 8 mol %. For example, the dielectric layer 510 is substantially free of nitrogen, while the nitridized oxide layer 410 a has a nitrogen molar percentage of about 2 mol % to about 8 mol %.

The nitridized capping layer 310 a and the nitridized oxide layer 410 a may protect the fins 220, 230 from oxidation during the annealing processes according to some embodiments. As discussed above, annealing processes may be carried out in order to improve the quality of the dielectric layer 510, in accordance with some embodiments. In the annealing processes, the semiconductor substrate is subjected into a surrounding at a temperature of several hundred degrees Celsius or even higher in certain cases. At such high temperature, the fins 220, 230 are possibly oxidized due to the diffusion of oxygen from the dielectric layer 510 to the fins 220, 230. The oxidation of the fins 220, 230 unfavorably degrades the characteristics thereof. The nitridized capping layer 310 a and the nitridized oxide layer 410 a may block oxygen from diffusion into the fins 220, 230, and therefore protect the fins 220, 230 from oxidation during the annealing processes.

Referring now to FIG. 1, the method 100 proceeds to operation 150 by removing a portion of the dielectric layer, a portion of the nitridized oxide layer, and a portion of the nitridized capping layer to expose a portion of the fin. In some embodiments, the operation 150 may include multiple etching processes to gain a desired etch selectivity, flexibility and etch profile. FIGS. 6 and 7 illustrate detail steps of the operation 150 according to some embodiments of the present disclosure, in which multiple etching processes are used.

As illustrated in FIG. 6, a portion of the dielectric layer 510 is removed such that a portion of the nitridized oxide layer 410 a is exposed. The removal of the dielectric layer 510 may include a dry etch, a wet etch, or a combination of thereof. In examples, the dry etching process may use etchant such as for example fluorine-containing gas (e.g. CF₄, SF₆, CH₂F₂, CHF₃, and/or C₂F₆), chlorine-containing gas (e.g., Cl₂, CHCl₃, CCl₄, and/or BCl₃), bromine-containing gas (e.g., HBr and/or CHBR₃), iodine-containing gas, other suitable gases and/or plasmas, and/or combinations thereof.

The nitridized capping layer 310 a and the nitridized oxide layer 410 a may mitigate or even resolve the “dishing” issue, in accordance some embodiments. During the annealing processes discussed above, nitrogen probably diffuses from the nitridized oxide layer 410 a to the dielectric layer 510. The diffusion of nitrogen to the dielectric layer 510 may undesirably change the etching rate of the dielectric layer, and that causes the “dishing” issue. In accordance with some embodiments of the present disclosure, the nitrogen concentration of the nitridized oxide layer 410 a is controlled within a certain range, and the diffusion of nitrogen from the nitridized oxide layer 410 a to the dielectric layer 510 may be restrained during the annealing processes. Therefore, during the etching of the dielectric layer 510, the remained dielectric layer 510 a may have a desired surface (e.g., substantially flat surface), and the “dishing” issue may be mitigated or even resolved.

As illustrated in FIG. 7, the exposed portion of the nitridized oxide layer 410 a and the portion of the nitridized capping layer 310 a thereunder is etched to expose portions of the fins 220, 230. For instance, the upper portions 224, 234 of the fins 220, 230 are exposed. In some embodiments, an identical etching process may be employed to etch both the nitridized oxide layer 410 a and the nitridized capping layer 310 a. The remained portions 320 a, 320 b of the nitridized capping layer 310 a constitute bottom capping structures 330 a, 330 b. The bottom capping structures 330 a, 330 b respectively wrap the lower portions 222, 232 of the fins 220, 230. Further, the bottom capping structures 330 a, 330 b are interposed between the remained portion 420 a of the nitridized oxide layer 410 a and the corresponding one of the fins 220, 230. In yet some embodiments, because of the characteristics of the materials of the nitridized oxide layer 410 a and the nitridized capping layer 310 a, the bottom capping structures 330 a, 330 b (e.g., remained portions 320 a, 320 b) include respective bases 322 a, 322 b and respective fringes 324 a, 324 b, in which each of the fringes 324 a, 324 b extends upwards from the top surface of the corresponding one of the bases 322 a, 322 b. In some examples, each of the fringes 324 a, 324 b has a height L1 ranged from about 1 nm to about 10 nm. For example, the height L1 may be about 2 nm, 4 nm, 6 nm, and 8 nm. In yet some examples, the width of each fringe 324 a, 324 b is less than the width of each base 322 a, 322 b. For example, the width of each fringe 324 a, 324 b is about 20% to 80% of the width of the corresponding one of the bases 322 a, 322 b, for example 30%, 40%, 50%, and 60%. In yet some embodiments, the bases 322 a, 322 b and fringes 324 a, 324 b are in contact with the corresponding lower portions 222, 232 of the fins 220, 230.

In accordance with some embodiments, during the etching of the nitridized oxide layer 410 a and the nitridized capping layer 310 a, the remained dielectric layer 510 a are partially etched to be an isolation feature 510 b between the fins 220, 230. In specifics, the thickness of the remained dielectric layer 510 a depicted in FIG. 6 is reduced to form the isolation feature 510 b in FIG. 7. In some embodiments, the top surfaces S1 of the isolation feature 510 b is substantially leveled with the top surfaces F1, F2 of the bases 322 a, 322 b of the bottom capping structures 330 a, 330 b. The fringes 324 a, 324 b of the bottom capping structures 330 a, 330 b protrude out the top surface S1 of the isolation feature 510 b.

In some embodiments, the remained portions 320 a and 320 b (e.g., the bottom capping structures 330 a, 330 b) of the nitridized capping layer 310 a include nitrogen, and the remained portions 320 a and 320 b of the nitridized capping layer 310 a have a nitrogen molar percentage of less than 12 mol %. For example, the nitrogen molar percentage of the remained portion 320 a and 320 b of the nitridized capping layer 310 a is ranged from about 2 mol % to about 8 mol %, such as 3 mol %, 4 mol %, 5 mol %, 6 mol %, and 7 mol %.

Referring now to FIGS. 1 and 8, the method 100 proceeds to operation 160 by forming a top capping structure over the bottom capping structure and covering a sidewall of the exposed portion of the fin. FIG. 8 illustrates the formation of top capping structures 710, 720 respectively on the bottom capping structure 330 a, 330 b. The top capping structures 710, 720 respectively cover the exposed portions (e.g., top portions 224, 234) of the fins 220, 230 according to some embodiments of the present disclosure. The top capping structures 710, 720 respectively cover the fringes 324 a, 324 b of the bottom capping structures 330 a, 330 b. In some embodiments, the top capping structures 710, 720 consists essentially of silicon and are substantially free of nitrogen. In some embodiments, the top capping structures 710, 720 may be formed by epitaxial growth processes, such as molecular beam epitaxial (MBE) processes, metalorganic chemical vapor deposition (MOCVD) processes, and/or other suitable epitaxial growth processes. Specifically, an identical component is included in the top portions 224, 234 of the fins 220, 230, the top capping structures 710, 720, and the bottom capping structures 330 a, 330 b. Therefore, the top capping structures 710, 720 may grow epitaxially from the top portions 224, 234 of the fins 220, 230 and the fringes 324 a, 324 b of the bottom capping structures 330 a, 330 b. The top capping structures 710, 720 may engage with the fringes 324 a, 324 b of the bottom capping structures 330 a, 330 b. In some embodiments, the top capping structures 710, 720 are merely formed covering the exposed portions of the fin 220, 230 and the fringes 324 a, 324 b, whereas the surface of the isolation feature 510 b is free of the epitaxial material of the top capping structures 710, 720. Besides epitaxial growth processes, the top capping structures 710, 720 may be formed by a deposition process and followed by a selectively etching process. Illustrative examples of the deposition processes include chemical vapor deposition (CVD) processes, sub-atmospheric CVD (SACVD) processes, flowable CVD processes, atomic layer deposition (ALD) processes, physical vapor deposition (PVD) processes, and/or other suitable process. In some embodiments, a boundary 712 may be presented between the top capping structure 710 and the upper portion 224 of the fin 220, and a boundary 722 may be presented between the upper portion 234 of the fin 230 and the top capping structure 720. According to one aspect, the top capping structures 710, 720 may prevent the component of the fin 220 from diffusion into a gate dielectric layer formed in subsequent processes.

After the operation 160 shown in FIG. 1, the method 100 may further include other operations or steps. In some embodiments, a second oxide layer 810 may be formed to cover the top capping structures 710, 720, as illustrated in FIG. 9. The second oxide layer 810 may cover the top capping structures 710, 720 as well as the surface S1 of the isolation feature 510 b. In some embodiments, the second oxide layer 810 may serve as a dummy gate dielectric layer. The second oxide layer 810 may be deposited or thermally grown according to acceptable techniques, in accordance with some embodiments. Additional processes may continue for the fabrication of one or more features on the structure illustrated in FIG. 9.

In accordance with another aspect of the present disclosure, a semiconductor structure is provided. FIG. 9 also illustrates a semiconductor structure 200 according to various embodiments of the present disclosure. The semiconductor structure 200 includes a substrate 210, fins 220, 230, bottom capping structures 330 a and 330 b, top capping structures 710, 720, bottom oxide wrapping layers 420 a and 420 b, and a top oxide wrapping layer 810.

The substrate 210 may be a semiconductor substrate, such as a semiconductor-on-insulator (SOI) substrate, a bulk semiconductor, or the like. Alternatively, the substrate may be a wafer, such as a silicon wafer. The SOI substrate may include a layer of a semiconductor material formed on an insulator layer. The insulator layer may be, for example, a silicon oxide layer, a buried oxide (BOX) layer, or the like. Other substrates, such as a multi-layered or gradient substrate may also be used. In some embodiments, the semiconductor material of the substrate may include silicon; germanium; a compound semiconductor including silicon carbide, gallium arsenic, gallium phosphide, indium phosphide, indium arsenide, and/or indium antimonide; an alloy semiconductor including SiGe, AlInAs, GaAsP, AlGaAs, GaInP, GalnAs and/or GaInAsP; or combinations thereof. In some embodiments, the substrate 210 has a PMOS region 212 and a NMOS region 214 thereon.

The fin 220 and the fin 230 are disposed on the substrate 210. The fin 220 has a lower portion 222 and an upper portion 224 extending upwards from the lower portion 222. The fin 230 has a lower portion 232 and an upper portion 234 extending upwards from the lower portion 232. In some embodiments, both the fins 220, 230 are made of silicon. In yet some embodiments, the lower portions 222, 232 of the fins 220, 230 include silicon or consist essentially of silicon with or without dopants, but the upper portions 224, 234 of the fins 220, 230 include silicon germanium or consist essentially of silicon germanium with or without dopants. In yet some embodiments, however, the material of the fin 220 formed on the PMOS region 212 may differ from that of the fin 230 formed on the NMOS region 214. Specifically, both the lower and upper portions 232, 234 of the fin 230 may include silicon or consist essentially of silicon with or without dopants, whereas the upper portion 224 of the fin 220 may include or consist essentially of silicon germanium while the lower portion 222 thereof may include or consist essentially of silicon with or without dopants. In some examples, the upper portion 224 of the fin 220 has a germanium molar concentration ranged from about 10% to about 35%, such as for example 15%, 20%, 25%, and 30%.

The bottom capping structure 330 a covers the sidewall of the lower portion 222 of the fin 220. Similarly, the bottom capping structure 330 b covers the sidewall of the lower portion 232 of the fin 230. In some embodiments, the bottom capping structures 330 a, 330 b include nitrogen. In some embodiments, each of the bottom capping structures 330 a, 330 b includes a silicon layer and nitrogen doped therein, and the nitrogen molar percentage of the bottom capping structures 330 a, 330 b is less than 12 mol %. For example, the nitrogen molar percentage may be ranged from about 2 mol % to about 8 mol %, such as 3 mol %, 4 mol %, 5 mol %, 6 mol %, and 7 mol %.

In some embodiments, the bottom capping structure 330 a includes a base 322 a and a fringe 324 a. Similarly, the bottom capping structure 330 b includes a base 322 b and a fringe 324 b. The fringes 324 a, 324 b respectively extend upwards from the bases 322 a, 322 b. Each of the fringes 324 a, 324 b has a width less than a width of each of the bases 322 a, 322 b. For example, the width of each of the fringes 324 a, 324 b is about 20% to 80% of the width of each of the bases 322 a, 322 b, such as 30%, 50% or 70%. In some embodiments, each of the fringes 324 a, 324 b has a height ranged from about 1 nm to about 10 nm, such as for example 2 nm, 4 nm, 6 nm, and 8 nm. In yet some embodiments, the base 322 a and the fringe 324 a are in contact with the sidewall of the lower portion 222 of the fin 220, and similarly the base 322 b and the fringe 324 b are in contact with the sidewall of the lower portion 232 of the fin 230. In yet some embodiments, top surfaces F1, F2 of the bases 322 a, 322 b are substantially leveled with the top surface S1 of the isolation structure 510 b.

The top capping structure 710 and the top capping structure 720 are respectively disposed over the first and second bottom capping structures 330 a, 330 b, in accordance with some embodiments. Further, both the top capping structures 710, 720 are disposed over the isolation feature 510 b. The top capping structures 710, 720 respectively cover the upper portions 224, 234 of the fins 220, 230. In some embodiments, the top capping structures 710, 720 consist essentially of silicon and are substantially free of nitrogen. In yet some embodiments, a boundary 712 may be presented between the upper portion 224 of the fin 220 and the top capping structure 710, and a boundary 722 is presented between the upper portion 234 of the fin 230 and the top capping structure 720.

In accordance with some embodiments, the bottom oxide wrapping layers 420 a, 420 b respectively cover the sidewalls of the bottom capping structures 330 a, 330 b. In some embodiments, each of the bottom oxide wrapping layers 420 a, 420 b has a nitrogen molar percentage ranged from 1 mol % to 12 mol %. For example, the nitrogen molar percentage of the nitridized oxide layer 420 a, 420 b may be about 2 mol % to about 8 mol %, such as 3 mol %, 4 mol %, 5 mol %, 6 mol %, and 7 mol %.

In accordance with some embodiments, the top oxide wrapping layer 810 covers the top capping structure 710, 720. The bottom oxide wrapping layer 420 a, 420 b include nitrogen while the top oxide wrapping layer 810 is free of nitrogen.

According to some embodiments, the semiconductor structure and the manufacturing method thereof provided herein are advantageous hi the improvement of the “dishing” issue of the isolation feature (e.g., STI), thereby improving the device performance. Further, the semiconductor structure disclosed herein may protect the fin structure from oxidation when annealing processes are performed, in accordance with some embodiments. In addition, the semiconductor structure disclosed herein prevents the material of the fin from diffusion to a surrounding dielectric.

In accordance with one aspect of some embodiments, a semiconductor structure includes a semiconductor fin having a lower portion and an upper portion, an isolation structure around the lower portion of the semiconductor fin, and a nitrogen-containing capping layer over a sidewall of the lower portion of the semiconductor fin. A top surface of the nitrogen-containing capping layer is higher than a top surface of the isolation structure.

In accordance with another aspect of some embodiments, a semiconductor structure includes a semiconductor fin having an upper portion and a lower portion, a first capping layer over a sidewall of the lower portion of the semiconductor fin, and a second capping layer over a sidewall of the upper portion of the semiconductor fin. A bottom surface of the second capping layer is lower than a top surface of the first capping layer.

In accordance with another aspect of some embodiments, a semiconductor structure includes a semiconductor fin having a lower portion and an upper portion, a first capping layer over a sidewall of the lower portion of the semiconductor fin, and a second capping layer over a sidewall of the upper portion of the semiconductor fin. The second capping layer is in contact with a top surface and a sidewall of the first capping layer.

The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure. 

What is claimed is:
 1. A semiconductor structure, comprising: a semiconductive fin having a lower portion and an upper portion; a nitrogen-containing capping layer at least partially extending along sidewalls of the lower portion of the semiconductive fin; and an isolation structure at least partially surrounding the lower portion of the semiconductive fin, wherein the nitrogen-containing capping layer is at least partially between the isolation structure and the sidewalls of the lower portion of the semiconductive fin, and a top of the nitrogen-containing capping layer is higher than a top of the isolation structure and lower than a top of the semiconductive fin.
 2. The semiconductor structure of claim 1, further comprising a bottom wrapping layer conformally over the nitrogen-containing capping layer.
 3. The semiconductor structure of claim 2, wherein the bottom wrapping layer comprises nitrogen.
 4. The semiconductor structure of claim 1, wherein the upper portion of the semiconductive fin comprises silicon germanium.
 5. The semiconductor structure of claim 1, wherein the upper portion of the semiconductive fin and the lower portion of the semiconductive fin are made of the same material.
 6. The semiconductor structure of claim 1, further comprising a nitrogen-free capping layer over a sidewall of the upper portion of the semiconductive fin.
 7. The semiconductor structure of claim 6, wherein the nitrogen-free capping layer is in contact with a sidewall of the nitrogen-containing capping layer.
 8. The semiconductor structure of claim 6, wherein the nitrogen-containing capping layer has a portion interposed between the upper portion of the semiconductive fin and the nitrogen-free capping layer.
 9. The semiconductor structure of claim 6, wherein a bottom of the nitrogen-free capping layer is lower than the top of the nitrogen-containing capping layer.
 10. The semiconductor structure of claim 1, wherein the nitrogen-containing capping layer is in contact with the sidewalls of the lower portion of the semiconductive fin.
 11. A semiconductor structure, comprising: a semiconductive fin comprising a lower portion and an upper portion; a first capping layer at least partially extending along sidewalls of the lower portion of the semiconductive fin, wherein the first capping layer comprises nitrogen; a second capping layer at least partially extending along sidewalls of the upper portion of the semiconductive fin, wherein the second capping layer is a silicon capping layer and is substantially free of nitrogen; and an isolation structure at least partially surrounding the lower portion of the semiconductive fin, wherein the first capping layer is at least partially between the isolation structure and the sidewalls of the lower portion of the semiconductive fin.
 12. The semiconductor structure of claim 11, wherein the first capping layer is in contact with the sidewalls of the lower portion of the semiconductive fin.
 13. The semiconductor structure of claim 11, wherein a bottom surface of the second capping layer is lower than a top surface of the first capping layer.
 14. The semiconductor structure of claim 11, wherein the second capping layer is in contact with the sidewalls of the upper portion of the semiconductive fin.
 15. The semiconductor structure of claim 11, further comprising a bottom wrapping layer over the first capping layer.
 16. The semiconductor structure of claim 11, wherein the first capping layer is in contact with the sidewalls of the upper portion of the semiconductive fin.
 17. A semiconductor structure, comprising: a semiconductive fin comprising a lower portion and an upper portion; a first capping layer at least partially extending along sidewalls of the lower portion of the semiconductive fin; a bottom wrapping layer over the first capping layer, wherein a top of the first capping layer is higher than a top of the bottom wrapping layer; an isolation structure at least partially surrounding the lower portion of the semiconductive fin, wherein the first capping layer is at least partially between the isolation structure and the sidewalls of the lower portion of the semiconductive fin, and the bottom wrapping layer is at least partially between the first capping layer and the isolation structure; and a second capping layer at least partially extending along sidewalls of the upper portion of the semiconductive fin, wherein a bottom of the second capping layer is lower than the top of the first capping layer.
 18. The semiconductor structure of claim 17, wherein the second capping layer is free of nitrogen.
 19. The semiconductor structure of claim 17, wherein the bottom wrapping layer comprises nitrogen.
 20. The semiconductor structure of claim 17, wherein the lower portion of the fin comprises Si and the upper portion of the semiconductive fin comprises silicon germanium. 